0

**注意：我需要进一步添加 NULLIF(0 或 5)。我在这里写了一篇关于我的回答的简短文章：http: //peterkellner.net/2013/10/13/creating-a-compound-nullif-in-avg-function-with-sqlserver/ 但对我的解决方案不满意）

我有一张结果表，与会者在其中输入课程的预计出勤率。如果他们输入 0 或将其留空，我想忽略它并获取输入值的平均值。如果没有整个 SQL 的 where 子句，我无法弄清楚如何将该约束添加到我的 AVG 函数中。那可能吗？我的代码如下所示：（EstimatedNumberAttendees 是我要追求的）。

SELECT dbo.SessionEvals.SessionId,
   AVG(Cast (dbo.SessionEvals.CourseAsWhole as Float)) AS CourseAsWholeAvg,
   COUNT(*),
   COUNT(case
           when dbo.SessionEvals.InstructorPromptness = 'On Time' then 1
           else null
         end) AS SpeakerOnTime,
   COUNT(case
           when dbo.SessionEvals.InstructorPromptness = 'Late' then 1
           else null
         end) AS SpeakerLate,
   COUNT(case
           when dbo.SessionEvals.InstructorPromptness = 'NoShow' then 1
           else null
         end) AS SpeakerNoShow,
   COUNT(case
           when dbo.SessionEvals.PercentFull = '10% to 90%' then 1
           else null
         end) AS PercentFull10to90,
   COUNT(case
           when dbo.SessionEvals.PercentFull = '> 90%' then 1
           else null
         end) AS PercentFullGreaterThan90,
   COUNT(case
           when dbo.SessionEvals.PercentFull = ' < 10% Full ' then 1
           else null
         end) AS PercentFullLessThan10,
   AVG(Cast (dbo.SessionEvals.EstimatedNumberAttendees as Float)) AS
   EstimatedAttending
FROM dbo.Sessions
 INNER JOIN dbo.SessionEvals ON (dbo.Sessions.Id =
 dbo.SessionEvals.SessionId)
WHERE dbo.Sessions.CodeCampYearId = 8
GROUP BY dbo.SessionEvals.SessionId
4

3 回答 3

2

AVG 忽略 NULL。因此，使其将 0 视为 NULL。为此使用NULLIF：

...
AVG(NULLIF(Cast (dbo.SessionEvals.CourseAsWhole as Float), 0)) AS CourseAsWholeAvg,
...
AVG(NULLIF(Cast (dbo.SessionEvals.EstimatedNumberAttendees as Float), 0)) AS EstimatedAttending
...
于 2013-10-10T20:02:02.783 回答
0

SQL AVG 函数默认会忽略空值，因此您只需要排除 0。您的 AVG 代码可以更改为以下内容：

AVG(nullif( Cast(dbo.SessionEvals.CourseAsWhole as Float), 0) AS CourseAsWholeAvg
于 2013-10-10T20:02:09.823 回答
0

您可以尝试使用内部查询来获取相同的会话，但排除零和空：

SELECT dbo.SessionEvals.SessionId,
   (
        SELECT AVG(SE1.CourseAsWhole)
        FROM dbo.SessionEvals SE1
        WHERE SE1.SessionId = dbo.SessionEvals.SessionId
        AND ISNULL(SE1.CourseAsWhole, 0) <> 0
   ) AS CourseAsWholeAvg,
   COUNT(*),
   COUNT(case
           when dbo.SessionEvals.InstructorPromptness = 'On Time' then 1
           else null
         end) AS SpeakerOnTime,
   COUNT(case
           when dbo.SessionEvals.InstructorPromptness = 'Late' then 1
           else null
         end) AS SpeakerLate,
   COUNT(case
           when dbo.SessionEvals.InstructorPromptness = 'NoShow' then 1
           else null
         end) AS SpeakerNoShow,
   COUNT(case
           when dbo.SessionEvals.PercentFull = '10% to 90%' then 1
           else null
         end) AS PercentFull10to90,
   COUNT(case
           when dbo.SessionEvals.PercentFull = '> 90%' then 1
           else null
         end) AS PercentFullGreaterThan90,
   COUNT(case
           when dbo.SessionEvals.PercentFull = ' < 10% Full ' then 1
           else null
         end) AS PercentFullLessThan10,
   AVG(Cast (dbo.SessionEvals.EstimatedNumberAttendees as Float)) AS
   EstimatedAttending
FROM dbo.Sessions
 INNER JOIN dbo.SessionEvals ON (dbo.Sessions.Id =
 dbo.SessionEvals.SessionId)
WHERE dbo.Sessions.CodeCampYearId = 8
GROUP BY dbo.SessionEvals.SessionId
于 2013-10-10T19:56:54.787 回答